Plasma levels and loss of antithrombin III in chronic ambulatory peritoneal dialysis and nephrotic patients.

Plasma antithrombin III (AT III) levels were measured as antigen concentration (radial immunodiffusion) and as heparin cofactor (amidolytic method) in 9 patients on continuous ambulatory peritoneal dialysis (CAPD). The loss of albumin, proteins, AT III antigen and AT III functional activity was calculated from the peritoneal dialysate and the corresponding serum levels were measured. The same determinations were performed on serum and urinary samples from 9 patients with nephrotic syndrome. Mean plasma levels of AT III antigen and AT III heparin cofactor in CAPD patients were normal, whereas nephrotic patients showed a reduction in these values within a wide range. However, the loss of AT III antigen was similar in both groups and was strictly correlated to the loss of albumin. Most AT III in the peritoneal dialysate from CAPD patients was still active, whereas in nephrotic patients only 26% of the excreted AT III was functionally active. The difference in plasma AT III was functionally active. The difference in plasma AT III levels between these two groups, in spite of the roughly similar amounts recovered in the dialysate and in the urine, might be explained by an additional AT III loss in nephrotic patients due to renal metabolism.